Slipstream MEG recovery packages use a regeneration section to remove water from an incoming rich MEG feed stream and produce a lean MEG stream. A portion of this lean MEG stream is routed to a reclamation unit or section where the salt component is removed to yield a salt-free, pH neutral, lean MEG stream. This salt-free lean MEG stream is then blended with the remaining lean MEG stream to produce a lean MEG product having up to 3 wt % dissolved salts and available for re-injection into the gas production line as hydrate inhibitor.
For gas fields where significant quantities of calcium and other divalent cations are present in the formation water, a calcium removal unit or section is located upstream of the regeneration section. The calcium is removed from the rich MEG stream by elevating the pH through the addition of sodium or potassium carbonates, hydroxides, or some combination thereof. The lean MEG exits the calcium removal section with an elevated pH, typically above 9.5.
Because carbonate and hydroxide are often added in excess of the required stoichiometric quantity, un-reacted carbonate and hydroxide is carried through the regeneration system and into the lean MEG product. Removal of water from the rich MEG in the regeneration section further elevates the pH of the lean MEG product sent for reinjection. Mixing this high pH lean MEG with the calcium-rich formation water in the gas production pipeline can lead to increased scaling of the pipeline by precipitation of, for example, calcium carbonate.
Therefore, a need exists to reduce the pH of the lean MEG product prior to injection and, in turn, mitigate pipeline scaling. Acidification of the lean MEG with hydrochloric acid (HCl) is an option but overdosing with hydrochloric acid can lead to rapid reduction in pH to levels at which corrosion of carbon steel pipework and vessels may occur.